Hi Frederick,

re:
> how did you make them fully smooth?

I turned on their control points and used Transform > Align to make these points all exactly in line:




> but I'm still running into some issues when adding fillets to my solid objects. See my latest posts for details.

I posted a reply above, but I'm having a hard time finding the location that matches your screenshots.

Like where is this one for example:



I think I found your #1 which is a normal result and I thought your #2 is here but your screenshot has a sharp corner while the model has a juncture patch:





It kind of makes it hard to answer your questions when the file is different than your screenshot.

- Michael